The symptoms are a large tan to light brown lesion or canker on the stem that usually surrounds a leaf petiole. The lesion is larger than that associated with Phoma and is lighter in color. There is usually more pith damage with Phomopsis compared Phoma. This is responsible for being prone to lodging.

Life Cycle: The fungus overwinters in infected plant debris. Ascospores are wind-blown or water splashed onto lower sunflower leaves. Infection moves in the leaf, to the petiole and then the stem.

Stalk infected with phomopsis

Damage: This infection usually becomes noticeable at or after flowering and is usually found in areas with high rainfall or under irrigation. NSA crop surveys show that Minnesota historically has the greatest infection of plants with 22% in 2007. Over the four year history of the survey, each state has reported some incidence of the disease. Several isolated fields in ND had an incidence of over 40% of the plants infected. The disease is most prevalent in areas with prolonged high temperatures and high rainfall. Yield loss can be quite extensive with lodging. Infected plants also have smaller heads and lighter test weight seeds.

Economic Thresholds: This is not well defined since there is not a fungicide treatment available.

Scouting Method: Not available

Management: There is no fungicide treatment available for this fungus. Crop rotation and resistant hybrids are the best tools. This disease has been most prevalent in Europe and seed companies have incorporated European resistance into some hybrids. Some seed companies rate their hybrids for Phomopsis resistance. Farmers in areas with a history of this disease should consider the tolerant/resistant hybrids.

Research: Work in the U.S. has been limited since much work is being done in Europe.